1. Field of the Invention
The present invention relates to an asynchronous transfer mode (ATM) switch, and in particular to a method for controlling the bandwidth and the quality of the ATM connection for an ATM switch.
2. Related Arts
Currently, next generation communication networks are gradually being introduced which employ asynchronous transfer mode (ATM) switches, for which ATM techniques are applied. ATM switching is a communication method employed for the transfer, using hardware switching, of data cells, each of which is composed of a predetermined series of 48 bytes to which is added a header comprising five information control bytes.
ATM switches are presently in widespread use for LANs/WANs and on the Internet, and it is expected that in the future they will be employed for other types of data exchange, such as VOD (Video On Demand).
FIG. 11 is a diagram illustrating the configuration of an ATM network system. In FIG. 11, a conventional telephone network, an Internet network and a VOD network are interconnected via ATM switches.
The employment of ATM switching is gradually being shifted away from its currently primary objective of providing PVC (Permanent Virtual Channel) services for dedicated lines and is increasingly being used to provide SVC (Switched Virtual Channel) services. For such a service, an ATM connection, which is set up each time a request is received from a subscriber, is an independent entity, and bandwidth and quality are controlled for each connection.
The facilities provided by VOD, which is a product of an ATM connection, and a broadcast multimedia service can be compared with a current television (TV) service by radio waves. Once a user powers on a television, with the facilities provided by the TV he or she can immediately view a program broadcast on a desired channel. And switching channels can be effected immediately by, for example, manipulating buttons on a remote controller. This is possible because since each channel employs an individual radio frequency band and uses the same bandwidth and transmission quality for simultaneous transmissions, a specific channel can immediately be selected merely by performing a frequency adjustment. However, when such an immediate channel switching VOD service has been provided via an ATM connection, the following problem has arisen.
FIG. 12 is a diagram for explaining a conventional ATM connection. In FIG. 12, for example, video data for a film are transmitted by a video server 2, which provides a film channel, via an ATM switch 1 to an STB (Set Top Box) 3, which is a subscriber terminal. With the service provided by VOD, when the STB 3 requests an ATM connection corresponding to a specific channel, the ATM switch 1 provides a link via a channel connection (VCCa), which is provided between the video server 2 and the ATM switch 1, to a channel connection (VCCc), which is provided between the STB 3 and the ATM switch 1, effected by an internal connection (VCCac) in the ATM switch 1 which controls the bandwidth and the quality of the channel connection.
The bandwidth is defined by, for example, a transfer speed (e.g., 1 Mbps), and the quality is defined by a cell loss ratio (e.g., 10xe2x88x9210).
When the STB 3 requests the switching of channels, as is shown in FIG. 12 the ATM switch 1 must change the ATM connection from a pre-switching channel connection (VCCa and VCCc) to a post-switching channel connection (VCCb and VCCd). Specifically, the ATM switch 1 must temporarily release the channel connection (VCCa and VCCc) and the internal connection VCCac, and then set up the internal connection VCCbd which is linked with the post-switching channel connection (VCCb and VCCd). The process of releasing the control of the bandwidth and the quality at the ATM switch 1 is required by the process for releasing the internal connection, and the setting of the bandwidth and the quality at the ATM switch 1 is required by the process for setting the post-switching internal connection. Thus, for these processes a specific period of time is required, and as a result, compared with the TV service, when channels for the VOD service are switched a time lag occurs that prevents channel switching from being satisfactorily performed.
One solution that has been proposed is for the ATM connection for all the channels to be set in a linked state in advance, so that at the ATM connection the switching of channels in a moment is possible. However, since in this case the bandwidth of the ATM connection would be wastefully employed, this is an unrealistic proposal.
It is, therefore, one objective of the present invention to provide an ATM switch for the switching in a moment of an ATM connection at the time channels are switched, and to provide a method for controlling the bandwidth and the quality of an ATM connection.
To achieve the above objective, according to the present invention, an ATM switch which forms ATM connection by linking an input connection with an output connection via an internal connection for controlling the bandwidth and the quality of the ATM connection, comprises:
an input line unit for terminating ATM cells input via the input connection;
an output line unit for outputting the ATM cells to the output connection; and
a switch unit for switching a first ATM connection formed by linking a first input connection with a first output connection via a first internal connection, to a second ATM connection, which has the same bandwidth and quality as the first ATM connection, formed by linking a second input connection with a second output connection via the first internal connection.
With this arrangement, when the first ATM connection is changed by channel switching to the second ATM connection, the first internal connection at the first ATM connection before the switching is employed for the linking of the second input connection with the second output connection at the second ATM connection. Therefore, the process for releasing the first internal connection and the process for setting a new internal connection are not required, and the ATM connection can be switched in a moment.
For example, the input line unit comprises a converter for converting input connection information included in the ATM cells input from the input connections into output connection information, and for obtaining a bandwidth and quality information for the ATM connection based on the input connection information. And the switch unit links the second input connection with the second output connection via the first internal connection in case that the bandwidth and quality information for the second ATM connection is the same as a bandwidth and quality information for the first ATM connection.
Preferably, the converter has a memory which stores table data for the output connection information and the bandwidth and quality information for the ATM connections which are set in accordance with the input connection information, and from which it obtains the bandwidth and quality information.
In addition, to achieve the above objective, a method for controlling the bandwidth and the quality for an ATM connection formed by linking an input connection with an output connection via an internal connection for controlling the bandwidth and the quality of the ATM connection, comprises the steps of:
linking a first input connection with a first output connection via a first internal connection for controlling the bandwidth and quality of a first ATM connection; and
linking a second input connection with a second output connection via the first internal connection when the first ATM connection is switched to a second ATM connection which has the same bandwidth and the same quality as the first ATM connection.
In addition, the method for controlling the bandwidth and the quality of the ATM connections may comprise the steps of:
obtaining a bandwidth and quality information for the first ATM connection and a bandwidth and quality information for the second ATM connection based on input connection information included in ATM cells input from the first and second connections respectively; and
comparing the bandwidth and quality information for the first ATM connection with the bandwidth and quality information for the second ATM connection.
The method for controlling the bandwidth and the quality of the ATM connections may further comprises the step of:
linking the second input connection with the second output connection via a second internal connection for controlling bandwidth and quality for the second ATM connection, when, at the comparison step, the bandwidth and quality information for the first ATM connection is different from the bandwidth and quality information for the second ATM connection.
Other features and advantages of the present invention will become readily apparent from the following description when taken in conjunction with the accompanying drawings.